An hydraulic cement is well known as a material which, when mixed with water and allowed to stand, will gradually set up as a hard, solid mass. Among the crystalline cements, Portland cement is probably the best known and most widely used.
In spite of its widespread use, Portland cement has recognized shortcomings in the areas of chemical durability and compatibility with thermal change. For example, solid structures produced by setting Portland cement tend to deteriorate under conditions of either very high or very low humidity. Accordingly, it has been proposed to employ certain silicate glasses in powder form as hydraulic cements. However, these glasses have yet to provide a degree of improvement necessary to warrant their cost.
There is a substantial interest in foamed inorganic materials because of the recognized limitations of organic foams where mechanical strength, resistance to heat, and/or resistance to combustion are requisites. Nevertheless, the crystalline cements, including Portland cement, have found little application in this area of material development. Portland cement, for example, can be foamed during the early stages of curing, but generates a foam that tends to be friable. Furthermore, the loss of water in the foaming process causes the strength of the foam to diminish.
Foamed glass products have been available for some time. These are customarily produced by mixing a powdered glass, or glass precursor, with a gasifying agent such as carbon or a carbonaceous material, the agent and glass being adapted to produce a gas by chemical or physical action as the glass is thermally softened. This operation of course contemplates temperatures approaching the glass melting range.
As a lower temperature alternative, various procedures have been devised for producing inorganic foams from alkali metal silicates. The resulting silica foams have been very useful, but tend to have low mechanical strength and to rapidly degrade under extreme humidity conditions. Thus, such foams could not be recommended for use either in an evacuated environment or in moist or wet areas.
It is then a primary purpose of this invention to provide an improved inorganic cement mixture, particularly adapted to production of foamed material, and products produced therefrom.